Use of lactobacillus case in immunostimulatory peptides

ABSTRACT

The invention concerns the use of  Lactobacillus casei  in a composition for oral administration to enhance immunity specific to pathogenic micro-organisms. Said composition can in particular be a food or a food supplement.

[0001] The invention relates to the use of lactic acid bacteria for potentiating the specific immune response against an infectious agent.

[0002] Lactic acid bacteria (LABs) are conventionally used to produce fermented food products, in particular dairy products.

[0003] The effects of lactic acid bacteria on the health were initially suggested by the studies of Metchnikoff (The prolongation of life. 1st ed. New York: GP Putman's Sons, 1908), and have since been the subject of many investigations.

[0004] It is now generally acknowledged that various lactic acid bacteria can exert a role which is beneficial to the health. These bacteria are also named “probiotics”, a name which denotes living microorganisms which, when they are ingested in sufficient amount, exert a positive effect on the health, beyond the conventional nutritional effects. Probiotic bacteria have in particular been described among species belonging to the genera Lactobacillus, Bifidobacterium, Streptococcus and Lactococcus, commonly used in the dairy industry.

[0005] Probiotics are thought to intervene in particular at the level of the intestinal flora by impeding the development of pathogenic microorganisms, and/or by acting more directly on the immune system. It has, for example, been observed that ingestion of probiotic bacteria or fermented foods, such as yogurt, comprising these bacteria, leads to a decrease in pathogenic bacteria; in terms of the immune system, various effects have been reported: an activation of the cells involved in the specific or nonspecific immune response, such as lymphocytes and macrophages, an increase in the level of immunoglobulins and in particular of IgA; an increase in the level of immune system-activating cytokines, etc. (for review, cf. for example MEYDANI and HA (Am J Clin Nutr, 71, 861-7217, 2000).

[0006] Overall, the studies carried out on various probiotic lactic acid bacteria tend to conclude that some species, or at least some strains of these species, have immunostimulatory properties. On the other hand, the mechanism(s) underlying these properties, and the components of the immune system potentially involved, remain uncertain. It therefore appears to be necessary to elucidate these aspects, in particular in order to propose better targeted applications of the various species or strains of probiotic bacteria.

[0007] Several studies carried out in humans and animals suggest that bacteria of the species L. casei have a beneficial effect on the health, and in particular a positive effect on the immune system.

[0008] Thus, it has been shown in mice that ingestion of fermented milk containing the L. casei strain DN-114 001 increases resistance to infection with Salmonella typhimurium [PAUBERT-BRAQUET et al. Int J Immunother, 4:153, (1995)]; activation of macrophages and an increase in circulating IgAs have been observed simultaneously.

[0009] The strain DN-114 001 was deposited, on Dec. 30, 1994, with the CNCM (Collection Nationale de Cultures de Microorganismes) [National Collection of Microorganism Cultures] held by the Institut Pasteur, 25 rue du Docteur Roux, in Paris, under the number I-1518; this strain, and the combination thereof with yogurt ferments for preparing fermented dairy products, are described in PCT application WO 96/20607 in the name of COMPAGNIE GERVAIS DANONE.

[0010] A recent study carried out in humans also reports that the consumption of fermented milk containing the L. casei strain DN-114 001 induces a reinforcement of resistance to Salmonella typhimurium. This effect is attributed to an action on nonspecific innate immunity [YOON et al., Int J Immunother; 15, 79-89 (1999)].

[0011] The inventors have investigated whether L. casei also has an action on adaptive immunity, which, unlike innate immunity, results in a specific immune response against a given pathogenic agent.

[0012] For this purpose, the inventors have studied the effect of L. casei, administered orally in vivo, on the ex vivo stimulation of T-cell proliferation in response to antigens representative of various types of common pathogenic agents: a bacterial antigen (tetanus); a fungal antigen (candida) and a viral antigen (influenza).

[0013] They have observed, for each of the antigens tested, that ingestion of L. casei leads to an increase in the proliferative capacity of T cells, and in particular of CD3⁺⁻ sub-populations, in response to activation with said antigen. This effect manifests itself more particularly in the case of the influenza antigen.

[0014] A subject of the present invention is the use of a bacterial strain of the species L. casei for preparing a composition which can be administered orally to reinforce a specific systemic immune response against a pathogenic microorganism.

[0015] This reinforcement of the immune response ensues from an increase in the proliferative capacity of the T cells specific for the antigens of said pathogenic microorganism.

[0016] According to a preferred embodiment of the present invention, said microorganism is an aerially disseminated pathogen, in particular a pathogen of the respiratory tracts.

[0017] The pathogens concerned are especially bacteria or viruses; among the latter, mention will be made, for example, of rhinoviruses, respiratory syncytial virus (RSV), and myxoviruses (orthomyxoviruses such as the influenza viruses (influenza type A, B or C), or para-myxoviruses, and in particular para-influenzae).

[0018] In the context of the implementation of the present invention, said L. casei strain may be used alone or in combination with other lactic acid bacteria of the species L. casei or of other species. Advantageously, it may be used in combination with yogurt ferments, namely Lactobacillus bulgaricus and Streptococcus thermophilus.

[0019] It may be used in the form of whole bacteria, which may or may not be live, and also in the form of a bacterial lysate, or in the form of bacterial fractions.

[0020] Preferably, a composition prepared in the context of a use in accordance with the invention contains at least 10⁵, preferably at least 10⁶, generally between 1×10⁸ and 1.5×10⁹ , L. casei cells per ml.

[0021] When L. casei is used in combination with yogurt ferments, said composition also advantageously comprises at least 10⁷, preferably between 2×10⁸ and 1×10⁹ , S. thermophilus cells per ml, and at least 5×10⁵, and preferably between 4×10⁶ and 2×10⁷ , L. bulgaricus cells per ml.

[0022] An L. casei strain most particularly suitable for use in the present invention is the CNCM strain I-1518.

[0023] Compositions prepared in accordance with the invention may be administered in the form of foods or of food supplements. They may, for example, be dairy products, and in particular fermented dairy products comprising at least said L. casei strain, optionally combined with other lactic acid bacteria, for example with yogurt ferments.

[0024] Compositions prepared in accordance with the present invention can be used in the context of the prevention and treatment of pathological conditions of infectious origin, and in particular of viral origin, and in particular of the flu. Preferably, in order to obtain an optimal effect, they will be administered for at least one week, and advantageously for at least 10 days, in an amount corresponding to the absorption of at least 10⁷, preferably at least 10⁸, generally between 10⁹ and 10¹² , L. casei cells.

[0025] The present invention will be more clearly understood with the aid of the further description which will follow, which refers to nonlimiting examples illustrating the properties of a Lactobacillus casei strain for reinforcing the specific response to microbial antigens.

EXAMPLE 1

[0026] Action of Lactobacillus casei on T-Cell Proliferation in Response to Antigenic Stimulation

[0027] A double-blind study versus placebo was carried out in order to test the effect of ingesting a fermented dairy product comprising the Lactobacillus casei strain DN-114 001 (CNCM I-1518) on T-cell proliferation in response to antigenic stimulation.

[0028] The conditions for this study are as follows:

[0029] Individuals

[0030] 88 healthy individuals, 18 to 50 years old, were recruited in the Department of Infectious Diseases, Washington Hospital Center (Washington D.C.). Individuals with a history of hepatitis or of renal problems, of cardiovascular dysfunctions, of immune or gastro-intestinal diseases, of severe asthma or of sugar diabetes, individuals having undergone treatment with antibiotics or immunosuppressors less than 3 months before the beginning of the study, individuals having a history of alcohol abuse or dependency, individuals with known intolerance or hypersensitivity to dairy products, individuals on a low-calorie diet, individuals having been vaccinated against the flu during the preceding season, and also pregnant women or women who were breastfeeding, were excluded from the study.

[0031] The protocol and the conditions of the study were approved by the Research Committee of the WHC, and also by the Institutional Review Board which controls studies carried out in humans.

[0032] The individuals selected were randomly divided up into 2 groups:

[0033] A group of 47 individuals (26 women and 21 men) received 100 ml per day of a fermented dairy product containing 2% fat, comprising yogurt ferments (L. bulgaricus and S. thermophilus) and the Lactobacillus casei strain DN-114 001, and marketed by DANONE under the trademark ACTIMEL.

[0034] A group of 41 individuals (22 women and 19 men) received a placebo for 28 days: 100 ml per day of milk diluted with water (⅕, v/v) supplemented with sugar to give it a calorific value equivalent to that of the ACTIMEL.

[0035] The individuals of the 2 groups were asked to refrain from consuming yogurt or other fermented dairy products for the duration of the study.

[0036] The mean (standard deviation indicated between parentheses) age of the individuals was 36 (7.3) and 32.7 (7.4), respectively, for the ACTIMEL group and the placebo group.

[0037] A blood sample (55 ml) was taken from each individual of the 2 groups before the start of consumption of ACTIMEL or of placebo, in order to determine the base values. The individuals were given control visits on days 9, 18 and 28, and completed a short questionnaire regarding their health, the possible side effects, and also the development of any illness possibly interfering with the interpretation of the results. A blood sample was taken during each visit for the purpose of immunological experiments.

[0038] For each individual blood sample, a complete blood cell count and a blood chemistry analysis were performed. In addition, a phenotypic analysis of the leukocytes and of the sub-groups thereof (T cells and sub-groups, B cells, monocytes and NK cells) was performed by flow cytometry.

[0039] Measurement of Cell Proliferation

[0040] The proliferative response of the T cells of the individuals of the ACTIMEL group and of the individuals of the placebo group, with respect to the three microbial antigens: candida, tetanus and influenza, was determined ex vivo by measuring ³HTdR incorporation as described below.

[0041] Preparation of Cells:

[0042] 30 ml of heparinized blood from each of the samples taken were treated as follows: the tube was centrifuged for 10 min at 1500 rpm. The plasma was carefully transferred into labeled cryotubes and stored at 70° C. [sic]. The blood was transferred into a 15 ml centrifuge tube and diluted to 1:3 with PBS. 10 ml of Ficoll-hypaque were added to a 50 ml centrifuge tube and covered with 30 ml of the diluted blood. The tube was centrifuged for 2 min at 2000 rpm at ambient temperature. The upper layer of PBS was drawn off and the mononuclear cells were pooled and transferred into a 15 ml centrifuge tube. 10 ml of HBSS were added, vortexed and centrifuged at 1500 rpm for 10 min; the supernatant was drawn off and the pellet was resuspended in 2-3 ml of HBSS. 8 ml of HBSS were added and the tube was centrifuged at 1500 rpm for 6 min. This protocol was repeated twice and the cells recovered were resuspended in 1-2 ml of PBS and then vortexed. The cells were counted, examining their viability by Trypan Blue exclusion, and the concentration thereof was adjusted to 2×10⁸/ml.

[0043] Preparation of Antigens:

[0044] Tetanus antigen: the preparation was carried out on the day of the assay. A stock solution was prepared by diluting tetanus toxoid (CONNAUGHT LABORATORY, Willowdale, Canada) to 1:1000 in PBS.

[0045]Candida albicans antigens: a stock solution was prepared by diluting Candida albicans antigens (BAYER CO, Elkert, Ind.) to 1:1000 in PBS.

[0046] Influenza antigens: a stock solution was prepared by diluting a preparation of influenza virus antigens (NIBSC, Herts, England) to 1:125 in PBS.

[0047] Microtitration plates (96 wells) were used. Each well received 100 μl of antigen stock solution and 100 μl of cells at a final concentration of 2×10⁵ cells per well Control wells received 100 μl of PBS instead of the antigen stock solution. The plates were incubated at 37° C., 5% CO₂ for 5 days; 18 hours before the end of incubation, 20 μl of 50 μCi/ml ³HTdR (NEW ENGLAND NUCLEAR, Boston, Mass.) were added. The cells from the wells of each plate were harvested on filters and these filters were counted directly in a MATRIX 9600 beta-counter (PACKARD INSTRUMENTS) in order to measure the ³HTdR incorporation, which is expressed in CPM (counts per minute).

[0048] For each individual of the group having received ACTIMEL and for each individual of the group having received the placebo, the proliferation is evaluated by determining the stimulation index (SI) according to the following formula: ${SI}:=\frac{{mean}\quad {CPM}\quad {stimulated}\quad {cells}}{{mean}\quad {CPM}\quad {unstimulated}\quad {{cells}\left( {{control}\quad {well}} \right)}}$

[0049] Statistical Analysis

[0050] Descriptive statistics (mean, standard deviation, median) were used to summarize the proliferative response of the T cells to exposure to each antigen, for each of the groups of the study at each measurement time. Due to the distribution bias of the proliferative response, transformation to natural logarithm was used for the proliferation data.

[0051] The variations in the proliferative response compared to the base value were used for the statistical modeling [LITTELL et al. SAS System for Mixed Model. North Carolina: SAS Institute Inc, (1996)]. The modifications in proliferative response compared to the base value, as a function of time, were represented using the curve smoothing technique as described by DIGGLE et al. [Analysis of Longitudinal Data. New York: University Press Inc, 1994].

[0052] A mixed linear model was developed to study the trajectory of the proliferative response. This model allows adjustment of the proliferation data to a quadratic curve for each group of the study.

[0053] This model is defined by the following equation:

Y _(ijt)=α_(ij)+β1_(j) T+β2_(j) T ²+ε_(ijt) , i=1, . . . n, j=1, 2, t=1, 2, 3, 4

[0054] in which:

[0055] Yijt denotes the variation in the proliferative response compared to the base value for the individual i in the product group j at time t; transformation to natural logarithm having been applied to each variable, Yijt=Log (proliferation at time t)−Log (base value);

[0056] αij denotes the interception for the individual i in the product group j. It reflects a random effect in the model. α_(ij)˜MVN (0, G), G contains the components of the variance in diagonal structure (MVN: multinormal variable distribution);

[0057] β1_(j) and β2_(j) are the regression coefficients of T and T² for the product group j;

[0058] T is the moment of measurement (day 0, 9, 18 or 28) and T² is the quadratic term of T.

[0059] ε_(ijt) is the error coefficient:

[0060] εijt˜MVN (0, R) and R=σ²I_(n), in which I_(n) denotes the identity matrix n×n.

[0061] Statistical tests for the following hypotheses were performed:

[0062] a) Test whether the estimated regression coefficient is 0.

H₀: β1_(j)=0 vs. H₁: β1_(j)≈0

[0063] (for a linear term)

[0064] and

H₀: β2_(j)=0 vs. H₁: β2_(j)≈0

[0065] (for a quadratic term)

[0066] If β1_(j) and β2_(j) are not different from 0, there is no trajectory.

[0067] If β2_(j) is significantly different from 0, there is a quadratic trajectory.

[0068] If only β1_(j) is significantly different from 0, there is a linear trajectory.

[0069] b) Compare whether the trajectories of the two groups are identical.

H₀: β1₁=β1₂ vs. H₁: β1₁≈β1₂

[0070] (for a linear term)

[0071] and

H₀: β2₁=β2₂ vs. H₁: β2₁≈β2₂

[0072] (for a quadratic term).

[0073] The SAS statistical package was used to carry out the analyses.

[0074] Results

[0075] Table I below gives the demographic data regarding the individuals and the evaluation of the base value for proliferation. TABLE I Placebo vs. Demographic data and ACTIMEL base values Placebo ACTIMEL comparison Sex Female 22 26 Chi-squared Male 19 21 test P = 0.826 Age Mean (SD)  32.7 (7.4) 36.0 ± 7.3 T-test Median 31 37 P = 0.038 Ethnicity White 26 25 Chi-squared Black 12 17 test Exact p- Other 3 5 value = 0.652 Leuko- Mean (SD) 5997 5810 T-test cytes (1451) (1399) P =0.540 Median 5992 5990 Lympho- Mean (SD) 1932 (567) 2009 (554) T-test cytes Median 1812 1993 P = 0.519 CD3⁺CD4⁺ Mean (SD)  865 (327)  907 (325) T-test Median 740 818 P = 0.546 CD3⁺CD8⁺ Mean (SD)  469 (205)  431 (181) T-test Median 417 403 P = 0.360 CD3⁺CD25⁺ Mean (SD)  380 (200)  408 (182) T-test Median 349 392 P = 0.489 CD3⁺CD45⁺ Mean (SD) 1384 (488) 1411 (434) T-test Median 1354 1382 P = 0.783

[0076] T-Cell Proliferation in Response to Specific Microbial Antigens

[0077] The means, standard deviations and medians of the ex vivo proliferation of the peripheral blood mononuclear cells (PBMCs) for each group (ACTIMEL and placebo), at the various sampling times, are given in Table 2 below. TABLE 2 Placebo ACTIMEL Day Day Day Day Day Day Day Day Antigen 0 9 18 28 0 9 18 28 Candida Mean 2.3 2.7 2.9 1.9 3.0 3.2 4.3 2.3 SD 2.0 3.1 4.1 1.2 3.4 3.5 5.6 2.6 Median 1.5 1.7 1.6 1.6 1.7 1.7 2.0 1.4 Tetanus Mean 7.3 11.8 7.9 8.7 8.4 8.7 10.3 7.8 SD 7.8 12.3 8.0 8.1 15.8 10.4 11.8 8.2 Median 5.2 6.3 5.1 6.7 3.5 5.2 5.0 5.1 Influenza Mean 14.2 21.7 17.0 17.3 13.0 19.7 20.3 13.9 SD 11.4 19.1 19.6 15.7 12.6 17.1 16.6 12.7 Median 11.1 16.5 9.8 12.0 9.6 16.9 17.0 11.0

[0078] There are no significant differences between the two groups of the study for the base values (day 0) for the proliferative response with respect to the three microbial antigens.

[0079]FIG. 1 illustrates the variations in the proliferative response over time for each antigen for the two groups of the study: ACTIMEL group: continuous line; placebo group: broken line.

[0080] The results of the statistical modeling are provided in Table 3 below. TABLE 3 Parameter Standard H₀ test: Comparison of Antigen Variable estimation error parameter = 0 the 2 curves Candida Placebo T 0.017 0.014 P = 0.232 H₀: β1₁ = β1₂ T² −0.0007 0.0005 P = 0.208 P = 0.540 ACTIMEL T 0.028 0.013 P = 0.030 H₀: β1₁ = β1₂ T² −0.0012 0.0005 P = 0.013 P = 0.458 Tetanus Placebo T 0.034 0.014 P = 0.022 H₀: β1₁ = β1₂ T² −0.0008 0.0005 P = 0.141 P = 0.630 ACTIMEL T 0.043 0.013 P = 0.001 H₀: β1₁ = β1₂ T² −0.0011 0.0005 P = 0.020 P = 0.626 Influenza Placebo T 0.022 0.017 P = 0.181 H₀: β1₁ = β1₂ T² −0.0004 0.0006 P = 0.475 P = 0.045 ACTIMEL T 0.068 0.015 P = 0.0001 H₀: β1₁ = β1₂ T² −0.0023 0.0006 P = 0.0001 P = 0.027

[0081] Candida:

[0082] In the ACTIMEL group, the base response 3.0±3.4 at day 0 increases to 3.2±3.5 at day 9, and 4.3±5.6 at day 18, and then falls to 2.3±2.6 at day 28 (Table 2). The coefficients estimated for the linear term T and the quadratic term T² are 0.028 and 0.0012, respectively (Table 3). The two values are statistically significantly different from 0 (p=0.030 and 0.013, respectively). These observations imply that there is a significant positive tendency for the variation in proliferative response to the Candida antigen. The proliferative response first increases and then decreases, as shown in FIG. 1a.

[0083] The placebo group shows a small change over the period of the study. The regression coefficients estimated for T and T² are 0.017 and 0.0007. These values are not significantly different from 0 (p=0.232 and 0.208, respectively). These observations indicate that there is no significant change in the proliferative response for the period of the study in the control group. As shown in FIG. 1a, the curve for the placebo group is flatter than the curve for the ACTIMEL group. Although the ACTIMEL group shows a significant trajectory, in contrary to the placebo group, the difference between the two curves does not reach the level of statistical significance (p=0.540 for T and p=0.458 for T², Table 3).

[0084] Tetanus:

[0085] For the ACTIMEL group, the response gradually increased from the base level up to day 18, and then fell. The regression coefficients estimated for T and T² are 0.043 and 0.0011, respectively (Table 3). These two values are significantly different from 0 (p=0.001 and 0.020, respectively). As in the case of Candida, the positive variation in proliferative response over the period of the study is significant for the ACTIMEL group. In the placebo group, the mean value increased from 7.3 at day 0 to 11.8 at day 9, then fell to 7.9 at day 18, and increased again to 8.7 at day 28 (FIG. 1b). Even with a non-significant coefficient for the second degree term, T² (−0.0008, p=0.141, Table 3), the significant estimated coefficient of T (0.034, p=0.022, Table 3) shows a trajectory effect. However, if the ACTIMEL group is compared with the placebo group, the statistical tests do not show any significant differences between the two curves (p=0.630 and 0.626 for T and T², respectively).

[0086] Flu:

[0087] The ACTIMEL group showed a clearer change than the placebo group. The mean value increased from 13±12.6 at day 0 to 19.7±17.1 at day 9, remained at this level to day 18, and fell to 13.9±12.7 at day 28 (FIG. 1c). The two coefficients estimated for T and T² are significantly different from zero (p=0.001). These statistics indicate that the positive change in proliferative response during the period of the study is significant (Table 2).

[0088] The placebo group showed variations similar to those observed for tetanus. The mean values increased to day 9, fell to day 18, and increased again to day 28 as illustrated in FIG. 1c. The two estimated regression coefficients are not significantly different from 0 (the p values are 0.181 and 0.475 for T and T², respectively), indicating that there is no significant trajectory of variations in proliferative response to the influenza antigen.

[0089] When the parameters estimated for the ACTIMEL group and the placebo group are compared, significant differences are observed, both for the linear parameters and for the quadratic parameters (p=0.045 for T and p=0.027 for T2) (Table 3). These conclusions indicate that the variations in proliferative response are significantly different between the two groups of the study.

EXAMPLE 2

[0090] Action of Lactobacillus casei on the Proliferation of T Lymphocyte Subsets in Response to Stimulation with the Influenza Antigen

[0091] The exact nature of the T subset(s) which respond(s) in vitro to microbial antigens is not known. Either each one of the specific subsets of T lymphocytes, such as those represented by the phenotypes CD3+CD4+, CD3+CD8+, CD3+CD25+, and CD3+CD45+, may be considered to be a primary responder, or these combined subsets may contribute to the total proliferative response to booster antigens.

[0092] Presupposing that specific lymphocyte subsets are the main responders to booster antigens, analyses using the statistical model described in Example 1 above were carried out for the T-cell subsets CD3⁺CD4⁺, CD3⁺CD8⁺, CD3⁺CD25⁺, and CD3⁺CD45⁺, in order to determine whether the proliferative response obtained for each of the 4 subsets differed significantly between the ACTIMEL group and the placebo group.

[0093] In these analyses, the values for the proliferative response initially based on the total PBMCs were converted, for each subset, into new values calculated according to the total frequency of CD3+CD4+, CD3+CD8+, CD3+CD25+, and CD3+CD45+ T cells in each blood sample. Next, statistical analyses were performed for each subset, as described in Example 1 above.

[0094] The means, standard deviations and medians of each of 15 the placebo and ACTIMEL groups, for the four lymphocyte subsets, are given in Table 4 below. TABLE 4 Placebo ACTIMEL Lymphocyte Day Day Day Day Day Day Day Day subset 0 9 18 28 0 9 18 28 CD3 + CD4 + Mean 101 149 113 125 87.4 131 133 107 SD 84.0 130 117 127 104 90.2 112 127 Median 72.8 111 74.5 91.0 63.0 103 92.0 64.5 CD3 + CD8 + Mean 192 268 251 251 230 301 365 244 SD 155 250 289 336 375 286 554 302 Median 167 218 140.5 168 105 180 214 126 CD3 + CD25 + Mean 250 377 260 354 177 267 310 270 SD 219 374 208 462 139 163 210 305 Median 185 263 228 247 159 262 251 177 CD3 + CD45 + Mean 63.5 87.6 73.0 76.2 52.1 78.7 87.1 69.1 SD 54.1 70.9 81.3 79.7 72.2 56.3 79.2 95.2 Median 47.5 66.6 43.1 51.4 34.0 64.0 67.8 41.0

[0095] The differences in the base values between the two groups of the study are not statistically significant.

[0096] Using the statistical model described in Example 1 above, the variations in proliferation relative to these base values, in response to the influenza antigen, were analyzed for each of the four lymphocyte subsets. FIG. 2 illustrates the variations in proliferation, on a logarithmic scale, for each of these subsets and for each of the two groups of the study.

[0097]

[0098] The results of the statistical modeling are given in Table 5 below. TABLE 5 Lymphocyte Parameter H₀ test: Comparison of subset Variable estimation (SE) parameter = 0 the 2 curves CD3 + CD45 + Placebo T 0.015 (0.016) P = 0.352 H₀: β1₁ = β1₂ T² −0.0003 (0.0006) P = 0.597 P = 0.015 ACTIMEL T 0.071 (0.015) P < 0.001 H₀: β1₁ = β1₂ T² −0.0024 (0.0006) P < 0.001 P = 0.016 CD3 + CD25 + Placebo T 0.024 (0.016) P = 0.144 H₀: β1₁ = β1₂ T² −0.0004 (0.0006) P = 0.463 P = 0.031 ACTIMEL T 0.071 (0.015) P < 0.001 H₀: β1₁ = β1₂ T² −0.0022 (0.0006) P < 0.001 P = 0.030 CD3 + CD8 + Placebo T 0.014 (0.017) P = 0.410 H₀: β1₁ = β1₂ T² −0.0003 (0.0006) P = 0.671 P = 0.013 ACTIMEL T 0.070 (0.015) P < 0.001 H₀: β1₁ = β1₂ T² −0.0024 (0.0006) P < 0.001 P = 0.012 CD3 + CD4 + Placebo T 0.022 (0.017) P = 0.203 H₀: β1₁ = β1₂ T² −0.0005 (0.0006) P = 0.436 P = 0.028 ACTIMEL T 0.072 (0.015) P < 0.001 H₀: β1₁ = β1₂ T² −0.0025 (0.0006) P < 0.001 P = 0.024

[0099] The proliferative responses for each of the four lymphocyte subsets are in agreement with those observed for the total PBMCs. During exposure to the influenza antigen, significant variations are observed in the ACTIMEL group for the four lymphocyte subsets. These variations can be represented as a quadratic function of time.

[0100] Small variations were observed for the four subsets in the placebo group.

[0101] In addition, the differences between the two groups were significant for all the lymphocyte subsets.

[0102] Conclusion

[0103] These results show, for the 3 antigens tested, an increase in the proliferative response induced by an antigen booster, which was greater in the ACTIMEL group than in the placebo group. In the case of the influenza antigen, the increase in the ACTIMEL group is statistically significant compared to that observed in the placebo group, both for the total PBMCs and for each of the T cell subsets CD3+CD4+, CD3+CD8+, CD3+CD25+and CD3+CD45+.

[0104] It therefore appears that the consumption of ACTIMEL induced, in the individuals concerned, an immunological priming in vivo, which led to an ex vivo response of their T cells to the microbial antigens, and in particular to the influenza antigens, which was better than that observed in the placebo group.

[0105] This increase in the response correlates with the frequency and the status of activation of the CD3⁺ T cells, and of the subsets thereof, in the individuals of the ACTIMEL group.

[0106] In addition, the positive correlation with the presence of the CD25 activation marker suggests the involvement of an in vivo activation of influenza-specific T cells expressing CD25 IL-2 receptors and capable of responding more effectively to the influenza antigens. The analysis of the T-cell subsets also suggests that the proliferative response probably involves both the CD4⁺and the CD8⁺ subset corresponding to the influenza antigen. The importance of the CD3⁺/CD8⁺ T subset in the analysis of the proliferation suggests the possibility of in vivo priming of the pool of influenza-specific CD8+ cytotoxic cells. 

1. The use of a bacterial strain of the species L. casei for preparing a composition which can be administered orally to reinforce a specific systemic immune response against a pathogenic microorganism.
 2. The use as claimed in claim 1, characterized in that said pathogenic microorganism is a pathogen of the respiratory tracts.
 3. The use as claimed in either one of claims 1 and 2, characterized in that said pathogenic microoganism is a virus chosen from rhinoviruses, respiratory syncytial virus and myxoviruses.
 4. The use as claimed in claim 3, characterized in that said virus is an influenza virus.
 5. The use as claimed in any one of claims 1 to 4, characterized in that said L. casei strain is the CNCM strain I-1518.
 6. The use as claimed in any one of claims 1 to 5, characterized in that said composition is in the form of a food or of a food supplement.
 7. The use as claimed in any one of claims 1 to 6, characterized in that said composition is in the form of a fermented dairy product. 